Gemini Observatory: Exploring the Universe, Sharing its Wonders

Disappearing Supernovae Stars

March 17, 2009

Figure 1: Pre- and post-images of the galaxy M 74 with inset showing close-up of area around SN
2003gd (indicated by arrow). Both images were obtained with the Gemini Multi-Object Spectrograph on
the Gemini North Telescope in Hawaii. Both color composite images were made from g’, r’
and i’ filtered images. Pre-supernova images were made in August 2001 and post-supernova
images obtained in September 2008. A publication-quality version of the pre-supernova image of M 74
is available here.

Figure 2 (from Science Express paper): Pre- and post-explosion images of the site of SN 2003gd taken with the HST WFPC2
and Gemini GMOS instruments (see Table 1 for details). (A) Pre-explosion WFPC2 F606W
image, with the previously identified progenitor object marked as Star A, and a nearby star
labelled Star C. (B) Pre-explosion Gemini GMOS i band image, with spatial resolution 0.57”,
in which the progenitor is detected. (C) Post-explosion Gemini GMOS i band image where a
single point source is not detected at the transformed position of SN 2003gd, with a limit on
any remaining SN flux of mi (AB) > 26.3. The image has a spatial resolution of 0.36” and
no point source is detected at the position of Star C, suggesting a negligible contribution in
the i-band from that star. (D) Pre-explosion image with the flux/PSF-scaled post-explosion
image subtracted. The residual object at the position of SN 2003gd is the progenitor, with any
contaminating flux from nearby stars subtracted. The object at the SN location, marked as Star
A, is consistent with single-star PSF (χ2 = 0.9) and has a Johnson-I magnitude 23.14 ± 0.08
(mi (AB) = 24.25 ± 0.04). In the bottom right hand corner a model single star PSF is shown. It
was determined by IS IS and is consistent with the source detected in this subtraction image.

In a paper published in the March 19, 2009 issue of Science Express, Justyn Maund and Stephen Smartt
present data from the Gemini Observatory and Hubble Space Telescope (HST) that confirms the
disappearance of the progenitors of two Type II supernovae (SNe).

The only other supernova progenitor of this sort known to have definitively disappeared was SN 1987A in the Large Magellanic Cloud, part of our Local Group of Galaxies. Because the identity of the stars found in pre-explosion images has now been confirmed, this work provides the important “nail in the coffin” that the now missing Red Supergiants were the progenitors.

The two supernovae, denoted 1993J and 2003gd, both had confirmed pre-existing progenitors identified from archival data which allowed the researchers to compare pre-supernova identification of the progenitor star with post-supernova observations. Maund and Smartt used a technique where images were taken after SN 2003gd had faded away, and the progenitor star was presumably missing, and subtracted from the pre-explosion images. Anything left over at the SN position corresponded to the real progenitor star. The Gemini observations of 2003gd are shown in Figure 1 which compares pre- and post-supernova views of the progenitor star’s region of the galaxy know as M-74 or NGC 628. Figure 2 shows the images from the Science Express paper with both the Gemini and HST data.

“This is the first red supergiant progenitor for a normal Type IIP supernova which has been
shown to have disappeared and it's at the low mass end of the scale for massive stars to explode as
supernovae,” said Maund. “So, it finally confirms that a standard prediction of a number
of stellar evolution models is correct.”

Red Supergiants are massive stars, like Betelgeuse in the constellation of Orion, that are at least
eight times more massive than the Sun and have 500 times larger diameter. They explode as
Supernovae once they exhaust their supply of fuel and can no longer hold themselves up against their
own gravity. Having exploded in 2003, the matter the was once inside the red supergiant progenitor
of SN 2003gd is now being dispersed in its host galaxy to help form the next generation of stars.

All of the data for the study of SN 1993J (located in the galaxy M-81 or NGC 3031) were obtained
with HST. The progenitor for this star was a binary system that exploded in a Hydrogen-bearing (Type
IIB) supernova.The star that exploded has now disappeared, but its companion star, which stole most of the mass from the progenitor, is still there in the debris of the SN explosion.

Justyn Maund is a researcher at the Dark Cosmology Centre, Niels Bohr Institute, University of
Copenhagen, Denmark and the University of California Santa Cruz. Stephen Smartt is at the
Astrophysics Research Centre, School of Mathematics and Physics, Queens’ University Belfast,
United Kingdom.

The Gemini Observatory is an international collaboration with two identical 8-meter telescopes. The Frederick C. Gillett Gemini Telescope is located on Mauna Kea, Hawai'i (Gemini North) and the other telescope on Cerro Pachón in central Chile (Gemini South); together the twin telescopes provide full coverage over both hemispheres of the sky. The telescopes incorporate technologies that allow large, relatively thin mirrors, under active control, to collect and focus both visible and infrared radiation from space.

The Gemini Observatory provides the astronomical communities in six partner countries with state-of-the-art astronomical facilities that allocate observing time in proportion to each country's contribution. In addition to financial support, each country also contributes significant scientific and technical resources. The national research agencies that form the Gemini partnership include: the US National Science Foundation (NSF), the Canadian National Research Council (NRC), the Chilean Comisión Nacional de Investigación Cientifica y Tecnológica (CONICYT), the Australian Research Council (ARC), the Argentinean Ministerio de Ciencia, Tecnología e Innovación Productiva, and the Brazilian Ministério da Ciência, Tecnologia e Inovação. The observatory is managed by the Association of Universities for Research in Astronomy, Inc. (AURA) under a cooperative agreement with the NSF. The NSF also serves as the executive agency for the international partnership.